A car navigation system mounted in a subject vehicle detects a current position of the subject vehicle to thereby show a map surrounding the current position on a display unit of the system. Here, this map is shown in two-dimensional expression, three-dimensional expression, or the like. In the three-dimensional expression that indicates both roads and buildings three-dimensionally, a road is sometimes hidden by a building or by an over-crossing overpass road. In this case, the hiding building or overpass road is shown in a transmission technique, so that the hidden road or portions can become visible, as described in Patent Document 1.
Patent Document 1: JP-2001-108458 A
In urban areas, an expressway is sometimes built as an elevated road over a usual city road, so the expressway as the elevated road and the usual road as a fly-under road, i.e., two parallel roads, run in vertically parallel with each other, in a vertical two-layered state.
On the map shown by the car navigation system, the two parallel roads are shown as two overlapped lines that indicate the two roads. This makes it difficult to determine which road of the parallel roads the subject vehicle travels, even though the current position of the subject vehicle is shown on the map. Further, typically, one line of the overlapped two lines indicating the expressway hides the other indicating the usual road. States of the fly-under usual road hidden by the elevated expressway cannot be thereby easily recognized, so the user feels inconvenient.
This problem can be experienced similarly in the following cases. First is that a wide bypass road adjoins, in parallel, a narrow usual road such as a service road. Second is that an underground road including half-underground road runs, in vertically parallel, under an aboveground or ground-level road.